1. Field of the Invention
This invention relates generally to spray guns or the like and more particularly to apparatus for spraying heat responsive materials.
2. Description of the Prior Art
Spray guns, of the type to which the present invention is directed, have many applications and there are many examples of such apparatus in the prior art.
For example, in U.S. Pat. No. 2,878,063, granted on Mar. 17, 1959, to F. P. Kish et al, there is disclosed a resin spray gun defined by a body having separate, serpentine, resin and catalyst passageways as well as a separate air passage. Means are provided for heating materials within the resin and catalyst passageways and a nozzle is secured to the body in order to define a mixing chamber having an outlet orifice that communicates with the mixing chamber. The resin and catalyst passageways are connected to the mixing chamber at a position opposite the outlet orifice and a baffle is disposed in the mixing chamber for intimately intermixing the fluids passing therethrough. The baffle is in the form of a wire brush having bristles that extend transversely to the direction of fluid flow and which contact the wall of the mixing chamber. In the Kish et al patent, a passageway for cooling the interior surface of the housing is not provided nor are means provided for maintaining a separation at the exit plane of the nozzle of the heated air and the material that is to be sprayed together with its carrier.
In U.S. Pat. No. 2,362,634 granted on Nov. 14, 1944, to W. M. Houghton, there is disclosed a conventional spray gun having a barrel on which is placed a heating coil for heating the coating material as it passes through the spray gun. Under normal, intermittent conditions of use, there are many times when the Houghton spray gun would be idle. Consequently, if the same quantity of heat is applied to the spray gun when it is idle as is supplied to it when it is in operation to liquify a coating material during its passage through the spray gun, the temperature may build up to such an extent that, during the succeeding spraying operation, the coating material may be overheated and thus spoiled or the spray gun may be damaged. Houghton attempts to overcome these problems by providing a valve for controlling the flow of the coating material. The valve is operable because the heating means in the spray gun maintain a substantially uniform temperature in the chamber irrespective of whether the valve is open or closed. However, Houghton does not provide means for maintaining the body of the spray gun in a relatively cool condition and, moreover, does not provide means for shielding the nozzle from the direct flow of the heated air.
Still another example of the prior art in the field to which the present invention is directed is disclosed in U.S. Pat. No. 3,677,471 granted on July 18, 1972, to S. T. Deakin. This patent discloses an apparatus and method for coating surfaces with a continuous unitary film of polytetrafluoroethylene by spraying a heated stream of particles from the spray gun. A heater in the form of an electrical resistance unit is provided as well as a mixing chamber where gas is mixed with the particles. Means are also provided for directing a stream of gas through the guns to force the heated particles onto the surface to be coated. Specifically, Deakin discloses a conduit for delivering a mixture of polytetrafluoroethylene particles to the surface to be coated through a nozzle. A cylindrical tube is mounted around the conduit and an electrical resistance heater is positioned around the tube for heating the particles by radiation. A reservoir is provided for holding a quantity of these particles and the conduit is connected to the reservoir at a position adjacent the lower level of the particles. A pipe having an exit port is connected to the reservoir for forcing gas through the particles and means are also provided in the reservoir for agitating the particles. Deakin does not provide a stream of cooling gas directly against the interior surface of the housing in order to maintain the housing in a relatively cool condition, nor does Deakin provide any form of shield or baffle to divert the heated air from the exit plane of the nozzle.
U.S. Pat. No. 3,217,274, granted on Nov. 23, 1965 to A. Roche, discloses a radially symmetrical spray gun for paint having a nozzle that includes inner and outer passages for paint and compressed air, respectively. A central heating chamber is used containing electrical heating means that are connected to the outer passage with the electrical heating means being disposed below the nozzle. There is also provided a paint conduit connected to the inner passage that feeds paint in a thin stream under pressure through a tortuous path to the inner passage. Hot air is fed through a conduit that is disposed axially adjacent, concentric and radially within the conduit and in communication with the outer passage. A paint warming chamber, enclosing the hot air conduit, is provided through which paint flows under pressure towards the paint conduit with the paint warming chamber being enclosed by a wall of a central hot air conduit. A central, annular heating chamber is also provided having perforated walls that communicate with the air conduit and through which the air and paint conduit pass upwardly through the annulus thereof. The air feed conduit and the outer passage surround the entire length of the paint conduit and the inner passage such that the paint is subjected to heating throughout travel along the paint conduit and the inner passage. It should be noted that Roch feeds the material to be sprayed along a tortuous path but does not feed cooling air along a tortuous path in order to maintain the exterior surface of the housing in a relatively cool condition. In the same context, it should also be noted that Roche does not heat the compressed gas as the compressed gas flows along several legs of a serpentine path. It will also be evident from a reading of the Roche patent that there are no provisions for baffle means that divert the heated air away from the exit plane of the nozzle.
U.S. Pat. No. 2,795,461 granted on June 11, 1957, to W. M. Durkin discloses a spray gun comprising an inner liner ,ember that is adapted to hold the material to be sprayed, a barrel portion, an outer container member that is spaced from the inner member and an electrical heating element disposed between the inner and outer members. Means are provided for conveying heat through the inner member to a nozzle. Durkin does not make provision for directing the flow of relatively cool gas along a serpentine path, the first leg of which is defined by the inner surface of the housing in order to maintain the housing in a relatively cool condition, nor does Durkin suggest any means for diverting the flow of hot air away from the exit plane of the nozzle.
In U.S. Pat. No. 2,905,234, granted on Sept. 22, 1959, to H. Scholz, there is disclosed apparatus for the automization and combustion of liquid fuels. There is provided a pre-atomizing chamber and an elongated tubular atomizing chamber that is positioned coaxially in front of the pre-atomizing chamber. A conically converging annular passage is connected to the atomizing and pre-atomizing chambers and means are provided for passing a liquid fuel and an atomizing gas into the pre-atomizing chamber. A tubular member coaxially surrounds the atomizing chamber and defines an annular passage that terminates as a conically converging portion at a burner mouth. A flow guide member conically tapered at its opposite ends surrounds the forward ends of the tubular atomizing chamber and is positioned in said annular passage which defines, with the conically converging portion at the burner mouth, a conically converging annular passage. A second flow guide member having a conically tapered rear and forward end is positioned with its rear end extending into the forward outlet of the atomizing chamber and defining therewith a conically diverging passage with its forward end extending outwardly in the burner mouth. Means are provided for passing an oxidizing gas to the annular passage towards the burner mouth. Means are also provided for heating the wall of the atomizing chamber. In the Scholz patent, water inlet and outlet means are provided in an outer jacket for maintaining the housing in a relatively cool condition. However, it will be noted, that in contrast to the present invention which will be described more fully hereinafter, the cooling material used in the Scholz patent is not used for either heating or carrying the material to be sprayed. Moreover, Scholz does not disclose any means for shielding the nozzle by diverting heated air from the exit plane thereof.
Still another form of prior art which is only somewhat analogous to the present invention is represented by the flameless electric torch manufactured by GTE Sylvania Inc. under part No. SNH-130538. In the Sylvania product there is disclosed an elongated, tubular heating element that is positioned within a housing such that incoming air follows a serpentine path in order to first maintain the housing in a relatively cool condition and then be gradually heated until it reaches its maximum temperature at the interior of the cooling element prior to discharge. While the Sylvania product provides a serpentine path for the incoming gas and does maintain the housing in a relatively cool condition, there is no provision for the admission and discharge of a material such as resin or resin mixture to be heated and sprayed. More specifically, since the Sylvania structure does not contemplate the spraying of a resinous mixture, it does not provide means for shielding the nozzle, from which the resinous mixture would ordinarily be discharged, from the hot gases emanating from the apparatus.